Most of us are aware of the enormous reserves of carbon in our atmosphere, yet under our feet the earth's soil contains almost three times as much CO2, absorbing about a quarter of all human emissions per year.
If the world gets 2 ° C or more warmer, we risk turning this vital sink into a carbon chute.
An updated model of the soil carbon cycle showed that such warming could release 230 billion tons of carbon dioxide, give or take 50 billion tons. And that's just from the top meter of soil, which contains about the same amount of carbon as our atmosphere.
That number is slightly less than what China has been throwing away since 1900, and slightly less than half the United States since 1900.
Limiting the model to such shallow depths may seem like an oversight at first, but by limiting their measurements, scientists have made it easier to model changes in the soil cycle. It also helped cut the uncertainty created by other similar models in half.
“We have reduced the uncertainty in this response to climate change, which is vital for calculating an accurate global carbon budget and successfully meeting the Paris Agreement goals,” says climatologist Peter Cox of the Global Systems Institute.
Although higher temperatures are known to increase decomposition and reduce the amount of time carbon spends in soil, it is still not clear how sensitive this system is to temperature changes.
Recent studies, for example, have shown that as permafrost thaws, higher temperatures stimulate plant growth, and spreading roots serve as a 'primer' for the permafrost as it thaws further.
“In order to achieve the goals of the Paris Agreement, it is necessary to understand and quantify the inverse relationship between climate and the carbon cycle,” the researchers of the new model write.
'Changes in soil carbon represent a particularly large uncertainty with the potential for significant carbon mass reductions to stabilize the climate in a 2 ° C global warming.'
Carbon in the earth's soil has been accumulating for thousands of years. If we lose it, we cannot get it back again.
The research was published in Nature Communications.
Sources: Photo: (Enrique Aguirre Aves / The Image Bank / Getty Images)
